Cerebrospinal fluid, typically abbreviated as CSF, is a fluid that protects the brain and spine and helps distribute nutrients to these structures. CSF is a clear, colorless fluid that is primarily produced by the choroid plexus and surrounds the brain and spinal cord. Hydrocephalus is a condition in which a patient accumulates an excess volume of CSF. This often results from an obstruction of the cerebrospinal fluid pathways or from an inability to absorb the necessary volume of CSF. Increased CSF production relative to absorption causes the ventricles to become wider or dilate to make room for the extra fluid. Hydrocephalus is usually accompanied by an increase in CSF pressure which can be measured with a spinal tap, also known as a lumbar puncture. A spinal tap is a procedure in which a needle is inserted into a space inside the spinal canal for the purpose of removing some of the CSF.
The treatment of hydrocephalus has conventionally involved draining the excess fluid away from the ventricles and rerouting the cerebrospinal fluid to another area of the patient's body, such as the peritoneal cavity. A drainage system, commonly referred to as a shunt, is often used to carry out the transfer of fluid. In order to install the shunt, typically a scalp incision is made and a small hole is drilled in the skull. A proximal, or ventricular, catheter is installed in the ventricular cavity of the patient's brain, while a distal, or drainage, catheter is installed in that portion of the patient's body where the excess fluid is to be reintroduced. Generally, the shunt systems include a valve mechanism that operates to permit fluid flow only once the fluid pressure reaches a certain threshold level. That is, fluid flows through the valve only when the fluid pressure overcomes the valve mechanism's resistance to open. Some valve mechanisms permit the adjustment, or programming, of the opening pressure level, or resistance level, at which fluid flow commences. These valve mechanisms can comprise a variety of configurations. For example, the valve mechanism can be configured as a ball-in-cone as illustrated and described in U.S. Pat. Nos. 3,886,948, 4,332,255, 4,387,715, 4,551,128, 4,595,390, 4,615,691, 4,772,257, and 5,928,182, all of which are hereby incorporated by reference.
In some cases, however, hydrocephalus is characterized by an increase in the volume of CSF and a dilating of the ventricles with only slight or no increase in CSF pressure. This condition is known as normal pressure hydrocephalus. Even without an abnormal increase in CSF pressure, the widening of the ventricles to make room for excess CSF volume can have a deleterious impact on certain brain structures.
Normal pressure hydrocephalus can be difficult to diagnose. In part, the condition is difficult to diagnose because tests used to scan inside the brain, such as CT or MRI imaging, do not show a pattern that definitively indicates that a patient's condition is normal pressure hydrocephalus. A classic triad of symptoms (gait disorder, dementia, and incontinence) is also used in normal pressure hydrocephalus diagnosis. CSF pressure dynamics assessment can also be used, however, there is no convenient equipment for tracking and analyzing CSF pressure over time or measuring its response to stimulus. Once diagnosed, normal pressure hydrocephalus can be treated with shunting generally as described above.